A cyclodextrin (hereinafter referred to as "CD") is a cyclic dextrin comprising plural glucose residues as bonded to each other by .alpha.-1,4-bonding. .alpha.,.beta.- and .gamma.-CDs are well known, each comprising 6, 7 and 8 glucose residues, respectively. Recently, for the purpose of improving (or elevating) the solubility of CDs, branched CDs each having a glucosyl or maltosyl group bonded thereto by .alpha.-1,6-bond have been prepared.
Such CDs and branched CDs have a cavity in the molecule and the inside of the cavity is hydrophobic. Therefore, they have an including function and have a property of including various oily substances therein. Since CDs and branched CDs have such a property, they are widely used in various fields of food industry, cosmetic industry, drug industry etc.
Recently, in the field of drug industry, saccharides have been noted to have specific cell recognizability, and for the purpose of reducing the influences of the side effects of drugs, a study of utilizing such saccharides as a sensor to the target cells for a drug carrier in a drug delivery system has been made. Mannose is well known to have strong affinity to various parts in living bodies.
Under the situation, the present inventors tried to synthesize hetero-branched CDs by transferring a mannosyl group to a branched CD, for the purpose of applying the including function of branched CDs and the characteristic of mannose to a drug delivery system. As a result, they have found that various commercial .alpha.-mannosidase are usable for producing hetero-branched glucosyl or maltosyl CDs in which a mannosyl group has been .alpha.-bonded by a transfer action to the side chain of glucosyl-.alpha., .beta. and .gamma.CD (hereinafter referred to as G1-.alpha.CD, G1-.beta.CD and G1-.gamma.CD, respectively) or maltosyl-.alpha., .beta. and .gamma.CD (hereinafter referred to as G2-.alpha.CD, G2-.beta.CD and G2-.gamma.CD, respectively) from an .alpha.-mannosyl compound. They have further found that .alpha.-mannosidase derived from Jack beans (Canavalia ensiformis) is usable for preferentially producing a hetero-branched CD in which one mannosyl group is transferred by .alpha.-1,6-bonding to the glucosyl group of the side chain of G1-.beta.CD or to the non-reducing terminal glucosyl group of the maltosyl group of the side chain of G2-.alpha.CD. On the basis of the findings, they have completed the present invention.